The present invention relates more particularly to a high-voltage pulse generator comprising a charge storage means, a high-voltage source able to charge the said charge storage means, a first photoconductor element connected firstly to the reference of the potentials and secondly to the said storage means, a second photoconductor element connected firstly to the said storage means and secondly to a useful load, a first light source able to deliver a light pulse to the said first photoconductor, a second light source able to deliver a light pulse to the said second photoconductor, and a means of synchronising the emission delay between the first light source and the second light source.
This type of electrical pulse generator is referred to as the frozen wave type and, in a known manner, makes it possible to obtain bipolar signals or alternating polarisation pulse trains of any duration in theory.
In this type of generator, the photoconductors used are semiconductor substrates of various natures. Those most usually employed are said to be functioning in “avalanche” mode.
The drawback of these photoconductor systems working in avalanche mode is the high temporal jitter that is conventionally too great to synchronise short (subnanosecond) pulses. This temporal jitter in the starting of the two waves greatly limits the possibilities of controlling the required bipolar signal, and therefore the spectrum of the latter.
In addition avalanche mode does not make it possible to obtain reproducible pulses because of the chaotic character involved in the phenomenon, which in addition limits the service life of the photoswitches by local destruction of the substrate (the phenomenon of filamentation in the avalanche systems).
In order to obtain high-power electrical pulses of short duration, typically around one nanosecond or below, it is known how to use optoelectronic switches.
The application FR 2 679 716 describes for example a system generating a pulse comprising a DC high-voltage source, a capacitor that is charged by the source and that is intended to be connected to a load by means of an electrical connection adapted to the load, and a passive semiconductor element forming a photosensitive switch that closes when the photoconductive element receives a light pulse, and which is open in the absence of a light pulse. The closure of this switch causes the discharge of the capacitor and therefore the formation of a high-voltage pulse that supplies the load. The integration and nature of the semiconductor element then make it possible to obtain good performance for the pulse, typically a pulse whose rise (or fall) time is very short and is equal for example to less than 100 picoseconds (ps) for 2 kV.
This device does however have a certain number of drawbacks.
First of all, it will be understood that the device described in the application FR 2 679 716 makes it possible to determine whether pulses are negative or positive, according to the polarisation of the high-voltage source. This leads to a distribution of the power of the spectrum of the pulse limited to the low frequencies and does not allow control and mastery of this spectrum.
However, it is advantageous to control the profile of the electrical spectrum according to requirements.
In particular, in the field of biology, if a high voltage is applied to living cells, the application of a solely positive or solely negative voltage may cause a bursting of the cell by the creation of a force field within the cell.
It would therefore be advantageous to remedy these drawbacks by proposing an electrical pulse generator in which the pulse could be successively positive and negative over the pulse time and for which it is possible to control the spectral profile of the signal generated, while keeping a very short pulse duration, typically subnanosecond for peak to peak voltages of 3 kV or more and with low optical energies in order to be able to add together the power of several generators.